A liquid seal type single-chip semiconductor pressure sensor constitutes part of a sensor unit as disclosed in PATENT DOCUMENT 1, for example. The sensor unit is disposed inside a pressure detection chamber to be formed inside a joint portion made of a metal. For example, main elements of the sensor unit comprise: a diaphragm supported inside the joint portion and configured to isolate the above-mentioned pressure detection chamber from a liquid sealing chamber to be described below; the liquid sealing chamber formed below the diaphragm and configured to pool silicone oil as a pressure transmission medium; a sensor chip disposed inside the liquid sealing chamber and configured to detect pressure fluctuation of the silicon oil corresponding to displacement of the diaphragm; a chip mounting member designed to support the sensor chip; hermetic glass designed to seal a circumference of the chip mounting member around a through-hole of a housing; and a terminal group configured to deliver an output signal from the sensor chip and to supply power to the sensor chip.
Regarding the sensor chip described above, there has been proposed a structure as shown in FIG. 10 of PATENT DOCUMENT 1, which comprises: a movable portion (a pressure detection portion) on which multiple pressure detection elements are integrally formed; an electronic circuit integrally formed on a base around the movable portion and electrically connected to the pressure detection elements; an oxide film covering upper surfaces of the movable portion and the base; and a metal thin film covering the entire oxide film except a portion of the oxide film corresponding to the movable portion. The metal thin film is formed by aluminum vapor deposition in order to prevent adverse effects from occurring in the electronic circuit. Also, the reason for constituting the metal thin film to cover the entire oxide film except the portion corresponding to the movable portion is to prevent a deterioration of characteristics of the pressure sensor.
Nowadays, electro-magnetic compatibility (hereinafter also referred to as EMC) with respect to an interfering electromagnetic wave is required of the above-described single-chip semiconductor pressure sensor as well.